﻿THE 
  BACTERIA 
  201 
  

  

  188. 
  How 
  bacteria 
  secure 
  their 
  food. 
  Since 
  they 
  are 
  so 
  sim- 
  

   ple 
  in 
  structure, 
  and 
  since 
  they 
  live 
  in 
  direct 
  contact 
  with 
  

   their 
  food 
  supply, 
  the 
  bacteria 
  absorb 
  their 
  nourishment 
  directly 
  

   through 
  their 
  cell 
  walls. 
  Different 
  kinds 
  of 
  bacteria 
  may 
  live 
  

   upon 
  different 
  kinds 
  of 
  organic 
  matter, 
  but 
  almost 
  every 
  kind 
  

   of 
  organic 
  matter 
  may 
  serve 
  to 
  nourish 
  some 
  kind 
  of 
  bacteria. 
  

   Certain 
  kinds 
  of 
  bacteria 
  can 
  thrive 
  only 
  in 
  absence 
  of 
  free 
  oxy- 
  

   gen, 
  and 
  a 
  few 
  others 
  can 
  construct 
  food 
  somewhat 
  as 
  green 
  

   plants 
  do. 
  It 
  must 
  also 
  be 
  noted 
  that 
  bacteria, 
  like 
  other 
  liv- 
  

   ing 
  things, 
  produce 
  and 
  excrete 
  substances 
  which, 
  if 
  retained, 
  

   would 
  be 
  injurious 
  to 
  them. 
  If 
  excreted 
  and 
  accumulated 
  

   about 
  the 
  bacteria 
  in 
  great 
  quantity, 
  these 
  substances 
  would 
  

   soon 
  kill 
  them. 
  If 
  a 
  jar 
  of 
  beef 
  broth 
  is 
  carefully 
  sealed 
  after 
  

   any 
  ordinary 
  bacteria 
  have 
  been 
  introduced 
  into 
  it, 
  there 
  will 
  

   at 
  first 
  be 
  a 
  rapid 
  increase 
  in 
  their 
  number, 
  and 
  the 
  liquid 
  will 
  

   become 
  clouded 
  with 
  the 
  organisms 
  and 
  their 
  products. 
  But 
  

   the 
  excretions 
  soon 
  accumulate 
  to 
  such 
  an 
  extent 
  that 
  the 
  

   bacteria 
  can 
  no 
  longer 
  grow. 
  They 
  become 
  dormant 
  or 
  may 
  

   die 
  and 
  settle 
  to 
  the 
  bottom 
  of 
  the 
  jar 
  or 
  collect 
  in 
  a 
  jelly-like 
  

   mass 
  at 
  the 
  surface. 
  

  

  189. 
  How 
  bacteria 
  reproduce 
  themselves. 
  When 
  in 
  favor- 
  

   able 
  nutrient 
  material, 
  bacterial 
  cells 
  divide 
  frequently. 
  A 
  

   plant 
  thus 
  forms 
  two 
  new 
  ones, 
  each 
  of 
  which 
  may 
  soon 
  (in 
  

   from 
  twenty 
  minutes 
  to 
  half 
  an 
  hour) 
  divide 
  again. 
  This 
  is 
  the 
  

   simplest 
  possible 
  method 
  of 
  reproduction, 
  consisting 
  merely 
  

   of 
  the 
  dividing, 
  or 
  fission, 
  of 
  a 
  single-celled 
  plant. 
  The 
  possi- 
  

   bilities 
  of 
  this 
  rate 
  of 
  reproduction 
  are 
  enormous. 
  If 
  all 
  con- 
  

   ditions 
  were 
  to 
  remain 
  entirely 
  favorable 
  for 
  reproduction, 
  a 
  

   bacterium 
  which 
  divides 
  but 
  once 
  an 
  hour 
  would 
  in 
  two 
  days 
  

   produce 
  offspring 
  numbering 
  281,500,000,000, 
  and 
  " 
  in 
  three 
  

   days 
  the 
  progeny 
  of 
  a 
  single 
  cell 
  would 
  balance 
  148,356 
  

   hundred- 
  weight." 
  1 
  Of 
  course 
  it 
  is 
  well 
  known 
  that 
  ordina- 
  

   rily 
  this 
  rate 
  of 
  reproduction 
  cannot 
  be 
  realized, 
  because 
  

   growth 
  conditions 
  do 
  not 
  remain 
  favorable. 
  The 
  food 
  supply 
  

  

  1 
  Jordan, 
  E. 
  0., 
  General 
  Bacteriology, 
  p. 
  62. 
  W. 
  B. 
  Saunders 
  Company, 
  

   1911. 
  

  

  